Other mistake: When Mr Tinkles & Co are in the car outside the flocking factory, you see them speeding around the corners wildly, but if you look on the floor there are already treadmarks from previous takes.

As Buddy walks out into the street at the start of the movie when the cat is playing dead, you can see several parked cars on the street behind him. When the van backs up to 'catnap' buddy, there are no parked cars. Then as the van drives off again, there is a different bunch of parked cars in the street.